Ultrasonic measuring gauges are commonly used to measure the thickness of a material, and to determine whether there are any structural flaws in the material. Such gauges can be used for, example, to measure the effects of corrosion or erosion on tanks, pipes or any solid material where access is limited to one side of the material.
FIG. 1 illustrates an example of the structural features of a known ultrasonic gauge 110. The known gauge 110 includes a probe part 114 at a lower end of the gauge which enables a probe 116 to be connected to the gauge 110. At an opposite end of the gauge 110, a display 115 is arranged for reading out measurements or other data. Switches 112, 113, 117 are also provided on the gauge 110 for controlling the operation of the gauge 110. The switches 112, 113 and 117 are shown external to the display 115 in FIG. 1. However, the switches 112, 113 and 117 and other controls can be provided on the display 115 in the form of a touch-screen display.
The probe 116 includes a transducer for transmitting ultrasonic waves to a surface of a material to be measured, and receiving ultrasonic waves reflected back from the material. Processing circuitry comprised in the gauge 110 computes the thickness of the material based on the transmitted and received ultrasonic waves. The existence of structural flaws in the material can be determined based on the measured thickness of one part of the material, as compared with the relative thickness of other parts of the material. For example, during a scanning operation, the processing circuitry within the gauge 110 can compile aggregate data including a maximum thickness value and a minimum thickness value while the probe 116 is dragged across the material in continuous, uninterrupted physical contact with the material. U.S. Pat. No. 5,009,103 is an example of a known ultrasonic measuring gauge for measuring the thickness of a material. The entire disclosure of U.S. Pat. No. 5,009,103 is incorporated by reference in its entirety.
During a measurement operation, a coupling gel is commonly applied to the surface of the material to be tested. The gel provides a medium through which ultrasonic waves can travel from the probe 116 to the material. During scanning operations involving rough and/or scaly surfaces of the material, the probe 116 is dragged across the surface of the material while the processing circuitry in the gauge 110 analyzes ultrasonic reflections from the material that are propagated back to the processing circuitry via the probe 116. During such scanning operations, the probe 116 is in physical contact with the material via the coupling gel. However, during scanning operations, the probe 116 can be become physically decoupled, that is physically separated, from the material, either due to the rough and/or scaly surface of the material or due to user operation.
FIG. 2 illustrates an example of a scanning operation using such an ultrasonic gauge 110 on a material having a non-uniform surface. For clarity of illustration, only the probe 116 of the gauge 110 is illustrated in FIG. 2 for scanning the surface of a material 210. As shown at point A in FIG. 2, the probe 116 is physically coupled to the material 210 and thus the processing circuitry of the gauge 110 will be able to determine the thickness of the material 210 at point A due to the reflection of ultrasonic waves from the material 210 at point A. At point B, however, the probe 116 becomes physically decoupled (i.e., physically separated) from the material 210 due to the ridge and subsequent crevice at point B. As noted above, the processing circuitry of the gauge 110 is configured to maintain continuous readings while the probe 116 is in continuous, uninterrupted physical contact with the material 210. For example, it may be desirable to determine the maximum and minimum thicknesses of the material between points A and E of FIG. 2. However, because the probe 116 has become physically decoupled from the material 210 at point B, the processing circuitry of the gauge 110 may reset the measurement session, such that only the maximum and minimum values between points A and B are recorded. Similarly, even if the probe 116 is physically coupled again to the material 210 after point B, the operator may physically decouple the probe 116 from the material 210 at point C due to the ridge at point C. Such a decoupling will again result in the processing circuitry to restart a new measurement session between only points B and C. At point D, the probe 116 can be physically re-coupled to the material 210 and obtain continuous measurements between points D and E. However, due to the physical decoupling of the probe 116 at points B and C, the processing circuitry of the gauge 110 may output three independent measurement sessions, that is, (i) from point A to point B, (ii) from point B to point C, and (iii) from point D to point E. Accordingly, if it desired to measure the maximum and minimum thicknesses continuously from points A to E, erroneous indications may result due to the physical decoupling of the probe 116 from the material 210.